To overcome deficiencies of existing measures of exercise tolerance, a 3-component, 2-stage self-paced walking test, the HEALTH ABC long distance corridor walk (LDCW) was developed and is being used in the HEALTH ABC study. Key features are the 2-min warm-up walk, in which the first 20m is timed, that also serves as a stepped-down test and the focus on distance (400m) in the second stage instead of time (e.g., 6min.). Pilot test findings indicated that a target distance encouraged greater effort independent of fitness or test order. More widespread adoption requires further validation and comparison with the current "gold" standard, max treadmill testing with measured O-2 consumption. This project aims to: (1) determine the relationship between performance on a standardized max treadmill test and performance ont he 400m conponent of the LDCW, including variation by fitness level, (2) obtain an estimate of VO-2 max from time to complete 400m, among other parameters (e.g., ending HR, weight, sex, age); (3) determine the need to increase test ceiling; (4) obtain additional data on the relationship between 20m walking speed, 2-min distance, and 400m time; (5) determine reproducibility over a short time period; and (6) evaluate the advantages of the LDCW over treadmill-based tests for measuring exercise tolerance in older adults. The subject population will consist of 15 men and 15 women, 60 to 80 years (5 men and 5 women from each age- and sex-specific tertile of VO-2 max and will be recruited from participants int he BLSA criteria for max treadmill testing. Subjects will be administered the HEALTH ABC LDCW two times on separate days as part of their regular visit for the BLSA, after they undergo treadmill testing. The primary outcomes are to provide: (1) a validated alternative to max treadmill-based tests of exercise tolerance that is safe and acceptable for use in longitudinal population-based studies of older adults and (2) equations for estimating VO-2 max from time to walk 400m applicable to older adults. We anticipate that validation of a low cost and safe alternative to treadmill testing will promote more widespread inclusion of exercise tolerance testing in studies of older adults and thereby facilitate increased understanding of the disabling process. In addition, the LDCW has the potential for use in clinical settings as an indicator of preclinical functional decline and for screening to identify those most in need of early intervention.